Further embodiments of the present invention can be found in the claims, in the description, and in the examples. The abovementioned features of the subject matter according to the invention, and the features thereof that will be explained below, can, of course, be used not only in the respective combination stated but also in other combinations, without exceeding the scope of the invention.
There are well-known polyisocyanate polyaddition products which are obtained by mixing (a) isocyanate with (b) compounds having groups reactive toward isocyanates, (c) catalysts, (d) if appropriate, blowing agent, and (e) if appropriate, further additives to give a reaction mixture and permitting the reaction mixture to complete its reaction to give the polyisocyanate polyaddition product, and there are also well-known composite elements involving said polyisocyanate polyaddition products with plastic. Mechanical stressing of said composite elements, if appropriate after exposure to a high temperature and humidity, frequently leads to undesired break-away of the plastics from the polyisocyanate polyaddition products. Break-away of the polyisocyanate polyaddition products from the other plastics, with resultant irreparable damage to the composite element, is not acceptable in particular for the use of such composite elements in automobile construction, where this type of stressing of these elements cannot be excluded.
In the sheathing of electrical conductors, the insulated conductors are sheathed by a second plastic, e.g. polyurethane. Said second plastic here has to adhere on the insulation, so as to ensure that the system is watertight longitudinally with respect to the arrangement of the electrical conductors. If the system here is not watertight, it is impossible, in particular in automobile construction, to ensure separation between a dry compartment and a wet compartment. If an electrical line is involved which leads to control-module boxes or fuse boxes, or if encapsulation of relays and plugs is involved, there is also the risk of electrical short circuits. Sheathing moreover provides mechanical protection of the individual contact parts to prevent damage to and depoling of these.
In order to improve the adhesion between polyisocyanate polyaddition product and plastic, adhesion promoters based on polyester polyalcohols are added to the reaction mixture. Components (b) to (e) are usually premixed in the form of polyol component for the production of composite elements. The actual production of the polyisocyanate polyaddition products then takes place via mixing of the polyol component with an isocyanate component which comprises isocyanates (a). This procedure simplifies the production of the polyisocyanate polyaddition product, since there are then only 2 components to be handled. Composite elements of this type are described by way of example in EP 1361239.
A disadvantage of the polyol component described in EP 1361239 is that this forms a metastable system at room temperature. If said polyol component is cooled to below about 14-18° C., a precipitate forms, and even if the polyol component is reheated to 25° C. it does not regain its homogeneity. However, if inhomogeneous polyol mixtures are used for the production of the polyisocyanate polyaddition product, the result is low-quality products which then in some cases do not have any adhesion at all to the plastic of the composite.
DE 100 22 276 and DE 100 22 280 disclose composite elements where the adhesion promoter is reacted together with isocyanate to give a prepolymer having hydroxy groups or, respectively, isocyanate groups, and this prepolymer is then added to the polyol component or, respectively, the isocyanate component. A disadvantage here is that a further operation is necessary in the production of the polyol component or, respectively, the isocyanate component. Furthermore, crystallization also takes place in the case of prepolymers comprising hydroxy groups and in the case of prepolymers comprising isocyanate, and the stability and homogeneity of the components and of the system are then at risk.